The laboratory has been focused during the last year on immune-mediated tumor cell destruction. Natural killer (NK) cells and cytotoxic T cells (CTL) lyse virally-infected and tumor cells by 2 main mechanisms:(1) the exocytosis of lytic granules and (2) the expression of cytotoxic molecules like tumor necrosis factor (TNF) or related molecules like Fas-ligand. The cytolytic granules contain a variety of unique proteins, including a pore-forming protein (perforin) and a family of serine protease enzymes (granzymes). We have further studied the expression of granzyme M (met-ase), a novel granzyme that we had previously cloned. Using a monoclonal antibody specific for granzyme M we have detected this granzyme in freshly isolated NK cells, NKT cells and T gamma delta cells by western blotting and immunohistochemistry. T alpha beta cells do not seem to express this granzyme even after activation. The expression pattern of Granzyme M contrasts with that of the other granzymes and perforin, which can be easily detected in activated T alpha beta cells. This suggests that Granzyme M may be involved in innate rather than adaptive immunity. We are trying to define the biological role of this enzyme. In addition, we have investigated immune-mediated destruction of a murine renal cancer Renca and various other murine tumor cells in more detail. Using activated T cells from gld x pfpko mice as effector cells, we could still demonstrate the lysis of certain tumor cells in long-term cytotoxicity assays. This suggests that T cells can use mechanisms other than Fas ligand or perforin/granzymes to lyse certain tumors. Furthermore, the lysis of the Renca tumor by gld x pfpko T cells was not blocked by caspase inhibitors. This is unusual, in that most death receptors of the TNF family signal through the caspases. The identity of these effector molecules and their mechanism of tumor cell lysis is currently under investigation. - Fas-ligand, granzyme, Interferon gamma, NK cells, Serine Protease,